1. Field of the Invention
The present invention relates to a hydrogen generator that generates hydrogen from a predetermined material containing hydrogen atoms.
2. Description of the Related Art
Fuel cells generate an electromotive force through the reaction of hydrogen and oxygen, which are supplied to an anode (hydrogen electrode) and a cathode (oxygen electrode) arranged across a hydrogen ion-permeating electrolyte layer. The supply of hydrogen fed to the anode is produced by chemical reactions, for example, reforming reactions of a predetermined material like methanol or natural gas provided as the fuel. The fuel like natural gas is decomposed to a gaseous mixture containing hydrogen through reactions expressed below:CnHm+nH2O→nCO+(n+m/2)H2CnHm+2nH2O→nCO2+(2n+m/2)H2
Direct supply of the gaseous mixture to the fuel cells lowers the hydrogen partial pressure on the electrodes to interfere with the reactions on the electrodes. The direct supply may also cause carbon monoxide to damage the electrodes and interfere with the stable reactions. The general procedure thus separates hydrogen from the gaseous mixture and supplies only hydrogen to the fuel cells. A hydrogen separation film that allows selective permeation of hydrogen, for example, a palladium thin film, is used for separation of hydrogen. A known separation mechanism causes the gaseous mixture to pass through a cylinder of the hydrogen separation film, so as to extract hydrogen out of the cylinder. Another known mechanism utilizes a laminate structure, which includes layers of porous body with a catalyst for reforming reaction carried thereon, hydrogen separation layers, and spaces that allow the flow of extracted hydrogen (for example, the mechanism disclosed in JAPANESE PATENT LAID-OPEN GAZETTE No. 6-345408).
The cylindrical mechanism is, however, rather complicated in structure and disadvantageously increases the manufacturing cost and the size of the whole system. The drawbacks of the laminate structure are insufficient strength and possible leakage of the material gas into hydrogen due to the poor sealing properties. The arrangement of enhancing the strength and the sealing properties, however, causes another disadvantage, that is, the bulky laminate structure.
The hydrogen separation film is very thin, so that a pinhole in or a partial damage of the hydrogen separation film may cause carbon monoxide to be leaked to the hydrogen extraction side. As a measure against such leakage, a reaction unit, in which methanation of carbon monoxide proceeds to prevent the electrodes from being poisoned with carbon monoxide, may be provided after the hydrogen separation film. This arrangement, however, makes the hydrogen generator undesirably bulky. This measure also requires independent temperature regulation means for accelerating the methanation, thereby making the structure of the hydrogen generator undesirably complicated.
Application of the fuel cells for the vehicles have been attempted for practical use. It is thus highly demanded to reduce the size and the manufacturing cost of the hydrogen generator while enhancing the reliability and the strength thereof.